Put the chicken, garlic, spring onions, pesto and egg yolk in a bowl, add seasoning, then mix together well. Divide into 4, then shape into thick burgers. Chill for 1 hour.
Heat the oil in a nonstick frying pan, add the burgers and fry for about 10–13 minutes, turning once or twice until golden brown and cooked through.
Split the ciabatta rolls in half and lightly toast the cut sides. Spread with mayonnaise, then add the salad and tomatoes to the lower half of each roll. Top with the burgers and the other half of each roll, and serve with oven chips.